Archive for the 'Foundation' Category

We ordered a radon test kit from the New York State Department of Health last month. The kit is small canister of charcoal that you open and place in the test area for several days. We let it sit for 4 days in our basement, then sent it off to the testing lab. The results came back about a week later.

For reference, the EPA defines the safe limit of radon gas at less than 4 picocuries per liter of air (pCi/L). Our result was 38.6 pCi/L, almost 10 times the limit, ouch!

We had been somewhat slow to get the basement tested for radon because we spent a great deal of time and care sealing everything in the basement. Our blower door test confirmed that we had done a good job overall. So we assumed we would have no problems with radon.

Unfortunately, the radon is getting in, and because the house is so tight, it’s not getting back out.

Thankfully, we installed vent piping under the slab and sub-slab insulation when we built the house. We capped it off at the surface hoping we wouldn’t have to use it.

How sub-slab radon mitigation systems work

A vent pipe installed below the slab and vented to the outside depressurizes the area below the slab. Radon gas will take the easiest route to the outside. Our vent pipe runs the full perimeter of the inside of the footing under both the slab and 6″ of XPS insulation (R-30).

The EPA recommends running the vent pipe up the center of the house to the outside because the warmth of the house creates a stack effect, inducing a natural draft in the pipe without using mechanical ventilation. Unfortunately this method also cools the house in the winter, something we hoped to avoid.

So rather than run the vent through the house, we ran our exit vent pipe through the footing to the outside of the foundation wall and capped it at surface level. We figured if/when we determined we had a radon problem, we would extend the vent pipe up outside the house, through the soffit, into the attic, connect to an inline fan and exit through the roof.

The fan will use energy continuously but at least it won’t be cooling the house in the process. The installation cost will be minimal since we did most of the hard work when we poured the foundation.

In hindsight, we should have found a way to integrate the vent into an outer wall where it could still be insulated from the interior space. Running the vent up the outside of the house will take some work to make it not look like a strange pipe on the side of the house. We’re going to try to disguise it as a gutter. We’ll have more info on the details and photos as we start work next month.

This week we finished installing the interior drainage plane for the foundation walls, insulating the floor under the basement slab and pouring the slab. We also framed out the first floor exterior walls. The weather held out till Saturday afternoon when a cold rain forced us to stop.

We used extruded polystyrene foam (XPS, the blue stuff) under the slab because of its greater compressive strength. We laid two layers of 2 inch foam, then a layer of 6 mil polyethylene as our radon gas barrier. We used acoustical sealant to attach the poly to the drainage plane on the wall to complete our radon gas barrier. Then we laid another 2 inches of XPS foam for a total for R30 under the slab. The top 2 inches of the foam lies on top of the footing. We placed another 2 inches of expanded polystyrene (EPS, the white stuff) on the walls sitting on top of the XPS foam. EPS is more environmentally friendly than XPS. This overlap isolates the concrete slab from the foundation and walls, keeping it dry and warm.

The concrete arrived Friday. They poured and leveled 4 inches of concrete on top of the foam. They also poured a small knee wall in the walkout area and the footings for the deck on the west side of the house.

Above, we raised the first floor exterior walls. You can now start to get a sense of the size of the space and the view out the framed openings. Of course it will feel a bit smaller when we frame up the interior walls, and smaller still when we put up the sheathing and finally the interior drywall. Now you can see the house when driving up the driveway.

We wanted to get the first floor deck on before we poured the slab in the basement to help protect the concrete from the sun. Now that the deck is complete we move to the basement.

We had several tasks. 1. Wrap the center concrete pier in 6″ of rigid foam (a total of R30). The pier was poured on 6″ of foam when we poured the walls. 2. Install a radon perimeter pipe and a floor drain pipe. 3. Spread 4″ of clean gravel to level the floor. (Yes, that’s a tractor in our basement!) 4. Tamp down the gravel (I love a good tamping). 5. Attach drainage plane to the interior of the basement wall. This allows any condensation or water to drain down the concrete walls and out over the footing. We’re using a material that is generally used on the exterior, but it will work well for us as a drainage plane and air seal to keep any radon gas out. 6. Install 4″ of rigid foam on the floor over the gravel, lay down our poly vapor barrier and tape and seal to drainage plane.

We still have to attach 2″ of foam to the walls and then (finally) install the last 2″ of foam on the floor. (Later we will add 9″ of cellulose to the walls.) Then we will be ready to pour 4″ of concrete for the floor slab.

The basement is the weak link in most homes. Its considered a conditioned space since there is usually no insulation between the first floor and the basement, but it is cool and damp in the summer and bleeds heat from the house in the winter. We will have an R30 floor and R40 walls to match the rest of the house. Our efforts should even out the temperature swings and lower the potential for moisture and mold problems even though we’re not directly heating or cooling the space.

Last week Joe and Warren installed the perimeter footing drain, 1000 gallon rain water cistern, assorted drain pipes and then back-filled around the foundation walls. Materials including the trusses, beams, lally columns and floor sheathing also arrived. We were ready for a full day of activities on Saturday because we knew Sunday would be rainy.

Although we don’t have a picture, we managed to install the sill plates with gaskets, main beam (a 32 foot LVL laminated beam) and all the back bay trusses before the rain started. The gaskets under the sill plate are part of our air sealing system.

Next week we hope to finish installing the cement filled lally columns in the basement, the front bay trusses and put down the first floor sheathing. It’s going to take shape quickly from here. Stay tuned.

That sums up our weekend. We bushed on 1 1/2 coats of waterproofing about 5 to 6 feet up, removed more form ties on the inside and dug out the perimeter drain areas. This week they are going to lay the drainage pipe around the footing and backfill 1/2 way up the wall. That will make it easier to apply the rest of the waterproofing and give us a place to stand when placing the first floor trusses next weekend. We’re moving at a brisk pace now.